In order to manufacture a concrete structure, in general, concrete is first placed in formworks installed at a predetermined position, and then, the formworks are removed after concrete is set to some extent and hardened. Thereafter, a curing sheet is attached to a concrete surface from which the formworks are removed, for a predetermined period, and concrete is wet cured so that a hydration reaction proceeds. Meanwhile, concrete used for placement has increased fluidity so that concrete can be filled in every corner of the formworks, and includes excess water in an amount more than necessary for initial hardening of cement. Thus, after concrete is placed, such excess water may aggregate on the concrete surface as bleeding water, resulting in an insufficient strength of the concrete surface, or formation of air bubbles (pockmarks) on the concrete surface.
Then, for example, Patent Literature 1 proposes use of a sheet in which many pores are punched so that bleeding water generated after placement can be discharged to the outside. On the other hand, demolded concrete set to some extent and hardened is required to be in a wet state on the surface thereof in order to promote a hydration reaction of cement and water. Consequently, curing water is supplied to the concrete surface, and also the concrete surface is covered with a non-punched sheet or an unwoven fabric, on the contrary to the stage immediately after placement (see, for example, Patent Literatures 2 and 3).